Generally, tractors for hauling trailers are provided in two basic configurations, i.e., a conventional configuration and a cab-over-engine (COE) configuration. The conventional configuration for tractors have the cab located directly behind the engine in a typical automotive fashion. The cab-over-engine configuration provides the cab compartment directly over the engine. The cab-over-engine configuration is popular with operators who haul very long trailers and desire the improved maneuverability that can be achieved with the shorter wheelbase of the cab-over-engine configuration. This configuration is also popular with operators who must operate in jurisdictions having overal tractor-trailer length limits that can only be met with the cab-over-engine configuration.
In both configurations, the cab compartment may include a passenger seat, a driver seat, and a sleeping bunk, wherein the sleeping bunk is located rearward of the driver and passenger seats. In conventional models, the sleeping compartment is normally a separate structure located behind the cab compartment. In cab-over-engine configurations, the sleeping bunk is integral with the cab compartment and is located directly rearward of the driver and passenger seats. In both configurations, it is desirable to provide a cab compartment that maximizes the riding and sleeping comfort of the driver. To this end, it is desirable to provide a flat floor in the cab compartment to enable the driver to stand upright.
Due to a steadily increasing interest in aerodynamic efficiency, roof-mounted aerodynamic devices, referred to as aerodynamic fairings, have been developed to allow smooth flow of air over and around the trailer. Most manufacturers provide aerodynamic fairings that are an integral part of the cab and sleeping compartments. The aerodynamic fairings typically increase the overall interior and exterior height of the cab and sleeping compartments thereby providing an increase in interior headroom. While the increase in headroom is sufficient to permit a driver to stand upright in conventional models, the location of the engine directly beneath the cab compartment of the cab-over-engine configuration results in an engine tunnel intermediate the driver and passenger seats of the cab compartment. Movement of the driver from the driver seat to the passenger seat in an upright position is prohibited by the engine tunnel. Accordingly, it is desirable to provide a tractor having a cab-over-engine configuration wherein the cab compartment has a flat floor so that an unobstructed pathway is provided between the driver and passenger seats of the cab compartment in addition to providing an unobstructed pathway between the driver and passenger seats and the sleeping bunk.
One prior art method for providing a cab compartment of a cab-over-engine configured tractor wherein the cab compartment has a flat floor and sufficient stand up headroom to provide an unobstructed pathway between the driver and passenger seats of the cab compartment is to simply increase the height of the cab until the floor line clears the top of the engine. Unfortunately, this results in an extremely tall tractor having numerous disadvantages. The overall size and weight of the tractor increases significantly thereby providing a fuel economy penalty when pulling trailers having a smaller aerodynamic cross-section than the tractor. Also, the added height makes cab ingress and egress more difficult and deteriorates ride quality. An additional difficulty is that the tractor can no longer be towed or decked for transport without exceeding legal height limits, a difficulty that is worsened by the additional exterior height resulting from the aerodynamic fairing.
Another prior art method for providing a flat floor in a cab-over-engine configured tractor is to provide a so-called "pancake" engine where the normal in-line engine is laid over on its side and is located low in the frame. The engine is turned around so that the transmission is forward. An output shaft runs alongside the engine and is driven by a reversing gear. The output shaft is coupled to an intermediate bearing that drives a second shaft which in turn drives the rear axle. This configuration is mechanically complex and for this reason not acceptable. The combination of the reversing gear and additional shaft reduces the overall fuel economy of the engine. Also, due to the added number and complexity of the devices in the drive train, the cost of repairs and frequency of necessary maintenance is increased. Accordingly, it is desirable to provide a cab-over-engine tractor having a flat floor and sufficient height in the cab compartment to enable a driver to stand upright without unnecessarily increasing the mechanical complexity of the engine drive train.